Electron beam pumped gas lasers are known in the art, see "Electron-Beam Excitation of the Nitrogen Laser" by Dreyfus and Hodgson, Appl. Phys. Let., Volume 20, No. 5, March 1972, pages 195-197 and "Relativistic Electron-Beam Pumped uv Gas Lasers" by the same authors in J. Vac. Sci. Technol., Volume 10, No. 6, November/December 1973, pages 1033-36. These devices include a field-emission diode to launch an electron beam for pumping purposes. Usually this requires a static pressure, in the diode of .ltoreq. 0.1 Torr. On the other hand, to excite the gas to a lasing state, static gas pressures in the range of 4-45 Torr appears to be most desirable. These conflicting requirements have been satisfied, typically, by including a thin metal foil to separate the electron-beam launching device from the lasing gas. In this fashion, static gas-pressure differentials were maintained.
The thin metal foil, however, introduces a number of problems, some of which are summarized below:
1. The foil lifetime is usually limited to &lt; 1000 operations and sometimes only one.
2. An electron beam exiting from the foil is not well collimated, a typical one mil foil produces a beam of angular spread on the order of 30.degree. .
3. Current densities are limited by damage to the foil whereas high current densities are desirable to promote self-magnetic or electrostatic field focussing and more efficient energy transfer via non-linear interactions.
4. Use of the foil required high voltage diode operations (&gt;200 KeV) since the beam has to traverse the foil whereas low energy beams (i.e., &lt; 100 KeV) would be simpler to generate.
5. Relatively low efficiency due to the difficulty of extracting energy from a high energy beam.
6. The difficulty in handling corrosive gases (such as xenon and fluorine mixtures) since these tend to destroy the foil.
Devices other than lasers employ electron beams traveling in a gaseous environment. For example, under certain circumstances it is advantageous to transport an electron beam in a gaseous atmosphere. The electron beam ionizes at least some of the gas; the resulting electrons are expelled by the beam, while the positive ions help to maintain the beam in an integral condition. In the past, the electron beam was coupled into the gaseous atmosphere through a thin metal foil or the equivalent. By employing the principles of the present invention, this foil also can be eliminated with concomitant advantages.
It is, therefore, one object of the present invention to eliminate the necessity for this foil, or other physical apparatus to segregate the electron beam launching means from the gas while at the same time providing for emission of the beam and sufficient gas density for lasing and/or transport. It is another object of the present invention to meet the foregoing objects by introducing a gas density discontinuity in an evacuated cavity which also includes an electron beam launching means, and energizing the electron beam launching means at a time when two regions exist in the cavity, a first region immediately adjacent to the electron beam launching means which is in a substantially evacuated condition, and a second region which includes sufficient quantities of gas to support effective lasing operation.
It is another object of the present invention to provide for effective launching of electron-beams into a gas filled region of a cavity without providing apparatus to physically segregate the gas filled region from the region wherein the electron beam is launched.
It is a further object of the invention to provide for two regions in a cavity including an electron beam launching means and for energizing the beam launching means when the region surrounding the same is in a substantially evacuated condition at the same time the other region has substantial gas densities therein.